1. Field of the Invention
This invention is related to the field of liquid expulsion devices wherein liquid is expelled out of a tank by a positive expulsion mechanism.
More particularly, this invention is related to a liquid expulsion device wherein a diaphragm or bladder is utilized, the diaphragm containing the liquid is subjected to external pressure, the pressure forcing the diaphragm to expel the fluid out of the tank, the diaphragm eventually conforming to the opposite wall of the tank.
2. Description of the Prior Art
Many companies, particularly those associated with the aerospace industry, have employed collapsible diaphragms in liquid storage expulsion tank systems of various configurations and modes of expulsion. The problem of expelling liquids in the space atmosphere is highly complex. The probability of diaphragm failure is high in state-of-the-art expulsion devices, especially during liquid expulsion when metallic bladders are used. For collapsible metallic diaphragms, the failure mode is cracking of the diaphragms after partial collapse, wherein buckling of the bladder prior to reversing causes seam formation of the excess diaphragm material which must open up again for complete diaphragm reversal. Feasibility is always questionable for metallic bladders and certain tank geometries. As the degree of bladder elasticity increases, such as an elastomeric bladder, the problem is minimized. However, since elastomers are reactive with commonly used aerospace propellants, non-reactive, non-elastomeric materials such as metals must therefore be used. Metallic bladders are particularly important when long-time storage conditions of the propellants are required. The closer a deflecting body approaches symmetry of deflection, the more uniform the stresses in the metallic membranes during deflection, and the higher the capability of diaphragm reversal without failure. The present invention teaches a means to accomplish symmetry of deflection of metallic diaphragms, such means being applicable to non-metallic diaphragms as well.
A number of patents have issued that disclose collapsible bladders to expel liquid within a tank. For example, U.S. Pat. No. 3,339,803 entitled "Fluid Storage and Expulsion System" discloses a spherical tank with an internal diaphragm which conforms to the interior wall of a tank. The collapse of the diaphragm or liner is controlled essentially by the configuration modifications to the basic diaphragm geometry. Devices such as rings attached to the outside of the diaphragm are used to control the collapse of the diaphragm during the expulsion cycle. The invention additionally describes different tank configurations such as the prolate tank (football shape) wherein the diaphragm traverses from one pointed end to the other. The diaphragm must initiate its collapse at the end where the diaphgram is inherently stiff; therefore, it is necessary to so configure the diaphragm to force the diaphragm to reverse during the expulsion cycle. The foregoing configuration control is diametrically opposed to the teachings of the instant invention. The present invention controls the collapse of the diaphragm by its basic geometry, i.e., the oblate spheroid shape wherein the diaphragm need not be specially configured or stiffened to control the collapse of the diaphragm.
U.S. Pat. No. 3,404,813 discloses a tank with a metallic bladder, the outer structural member of the tank being essentially a sphere. Within the tank is a bladder which is adapted to collapse around an internal framework, the framework having curved bars radially extending from a center feeder tube, the bars being 120 degrees apart. Pressure between the interior wall of the sphere and the exterior surface of the bladder causes the bladder to collapse inwardly around the radially extending bars, thereby forcing the liquid into the center pipe and out of the expulsion device.
The above-described invention is disadvantaged in that the rigid support structure positioned within the flexible bladder merely controls the ultimate shape of the expulsion bladder when it has expelled all of the liquid from the interior thereof. There is no control of the collapse of the expulsion bladder during the initial and intermediate stages of the expulsion process. Therefore, the bladder takes on any number of random shapes during the early expulsion cycle, especially when the expulsion bladder is contained within a missile that is subjected to maneuvering acceleration forces. Liquid is oscillated from one side to the other, or skewed, while the missile is subjected to translational or pitching maneuvers along its flight path. A spherical diaphragm has a constant curvature; therefore, the collapse of the bladder is indiscriminate. It can start anywhere, perhaps several places at once.
Similarly, a prolate spheroid (football shape) is circular in a plane perpendicular to its major axis, its axis of rotation, and therefore has the same undesirable characteristics as the sphere in that its curvature is constant so that the diaphragm or bladder collapse can start at any point along its circular periphery. In the plane which depicts the elliptical shape, the curvature decreases at the ends of the major axis and is, therefore, stiffer at the ends. A symmetrical deflection results, the largest deflection and starting point being in the circular plane of the largest circle at the mid-point of the major axis.
The same asymmetric deflection characteristics are also present with cylindrical bladders with partially restrained ends. For example, another prior art invention, U.S. Pat. No. 3,722,751 entitled "Control-Fold Liquid Expulsion Bladder", assigned to the same assignee as the present invention, describes an expulsion bladder which consists of a liquid expulsion tank having two or more liquid-containing lobes circumferentially placed around the interior of a tank. For example, a three-lobe expulsion tank comprises an inner support structure forming three bays, each bay having a concave shape which is symmetrical to the outer tank walls surrounding the support structure. Between the inner wall of the tank and the wall of the support structure are located three metallic bladders that conform to the shape of each lobe of the tank. Each of these bladders is filled with a liquid propellant and the bladders conform to the walls of the central support structure and the inner wall of the outside containing tank. Gas under pressure is admitted to the area between the inner wall of the tank and the outer wall of the bladder so as to cause the bladders to deflect or buckle radially inwardly toward the center of the support structure. In order to control the collapse mode of each of these bladders, when they are subjected to external gas pressure, i.e., where the collapse starts, and how it reverses in a predictable manner, the wall thickness of the bladder is varied. The variable wall thickness assigned to specific areas on the bladder surface is the only mechanism which assures that the bladder collapses uniformly inwardly while expelling the liquid contained therein. However, initial collapse of a bay may start anywhere along the length of the bay, thus control of the collapse is somewhat uncertain.
Yet another U.S. Pat. No. 3,504,827, teaches a substantially cylindrical expulsion tank with an inner half metallic bladder connected along a longitudinal center line plane, to the inner surface of the cylinder. The outer wall of the bladder containing fluid is subjected to an outside source of pressurant. Pressure is admitted between the inner wall of the tank and the outer wall of the bladder causing the bladder to collapse toward the opposite inner wall of the tank, thereby expelling the fluid from the tank. This invention is subject to random, asymmetric buckling and bladder folding during tank manipulation as heretofore described with respect to the foregoing prior art patents.